Vibration responses and reminders. Two different things. Related. Vibrate isn't fixed, but should mean something, feel like a click when a click, feel harsh when "bad" feel soothing when "good" etc. Right now, on most devices, the vibrate device is a motor with an off-center weight. Very inefficient, so very power consuming. Keep this in mind when planning lots of haptic feedback... LOOK UP IF THERE ARE BETTER ONES THAT ARE COST EFFECTIVE. Also, can sometimes cheat with audio, make the speaker do low-tones and it's felt...
Emphasis - hit a key, it confirms by buzzing or clicking
Response - delay... you do something and it vibrates to say "okay"
Do not over-use haptic output without a good understanding of the device hardware. If traditional motor-driven vibration is used, it may consume the battery excessively quickly. D